Shares of Alignment Healthcare fell after one of its 2027 Medicare Advantage contracts received a 3.5-star rating from the Centers for Medicare & Medicaid Services, according to the company.

The stock slipped 21%, to $6.90, after-hours Thursday. It closed 1.9% higher, at $8.71, but has fallen 56% this year.

The 3.5-star rating, part of CMS's annual ratings of Medicare Advantage plans, was given to the company's California H3815 HMO contract.

"Alignment believes the rating does not accurately reflect the contract's longstanding performance on evidence-based measures of quality, clinical outcomes and member experience," the company said.

Dawn Maroney, the chief executive officer of Alignment Health Plan, said the company supports measuring the quality of health plans but called into question CMS's methodology.

"We intend to pursue all available administrative remedies and to litigate the measures and methodologies we believe warrant review," she said.

"At the same time, our strategy remains unchanged, and we remain confident in our ability to deliver exceptional care and return our California HMO contract to at least a 4-Star Rating," she added.

Alignment's other six Medicare Advantage contracts eligible for ratings earned at least four stars, with three plans being given 4.5-star ratings.